Magneto-optical recording medium and recording/reproducing apparatus therefor

ABSTRACT

A magneto-optical recording medium includes a reproducing layer. When a laser beam is irradiated to the magneto-optical recording medium, a magnetic domain in a recording layer is transferred, through enlargement, to a reproducing layer increased in temperature. The magneto-optical recording medium further includes a calibration area that has a calibration magnetic domain recorded in a predetermined pattern in the recording layer. In a reproducing apparatus, a laser beam of an optical head is adjusted in output depending upon a reproduced signal obtained by reproducing the calibration magnetic domain.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a magneto-optical recording medium andrecording/reproducing apparatus used therefor, and more particularly toa magneto-optical recording medium having a recording layer and areproducing layer so that microscopic magnetic domains can be recordedwithin the recording layer during recordation and the magnetic domainsthus recorded are magnified and transferred to the reproducing layerduring reproduction, and a recording/reproducing apparatus usedtherefor.

[0003] 2. Description of the Prior Art

[0004] There are magneto-optical recording mediums andrecording/reproducing apparatuses of this kind disclosed as examples,e.g. in Japanese Laying-open Patent Publication No. H6-295479 (Oct. 21,1994), G11B 11/10, Japanese Laying-open Patent Publication No. H8-7350(Jan. 12, 1996), G11B 11/10, and so on.

[0005] The magneto-optical recording medium 10 includes a recordinglayer 14 and a reproducing layer 16 each formed by a magnetic layer on asubstrate 12, as shown in FIG. 1. The recording layer 14 and thereproducing layer 16 have an intermediate layer 18 therebetween. Aprotecting layer 20 is formed on the recording layer 14. Incidentally,the intermediate layer 18 herein is formed by a non-magnetic layer, butcan be by a magnetic layer. Meanwhile, the recording layer 14 and thereproducing layer 16 can be desirably formed of a known magneticmaterial.

[0006] Referring to FIG. 2, microscopic magnetic domains (hereinafterreferred to also as “record magnetic domains”) 22 are recorded withinthe recording layer 14 of this magneto-optical recording medium 10 byusing a magnetic head (not shown). During reproduction, the recordmagnetic domain 22 in the recording layer 14 is transferred to thereproducing layer 16 by irradiating a laser beam 24 as shown in FIG. 3.More specifically, the laser beam 24 has a temperature profile as shownin FIG. 3, wherein the temperature assumes a maximum at and close to aspot center and gradually decreases toward the outside. However, wherethe magneto-optical recording medium is for example an optical disc, thetemperature profile on the magneto-optical recording medium is differentin slant at between the frontward and the rearward with respect to amoving direction. That is, the slant is more abrupt at the rearward thanthe frontward. By utilizing such a temperature profile by the laser beam24, the magneto-optical recording medium 10 is raised in temperature atonly a desired point thereof.

[0007] Returning to FIG. 2(A), if a laser beam 24 is irradiated to themagneto-optical recording medium 10, the magneto-optical recordingmedium 10 is increased in temperature according to a temperature profileas shown in FIG. 3. Here, the reproducing layer 16 is formed of amagnetic layer assuming rich in sub-lattice magnetization of transitionmetals and as a magnetic thin film with perpendicular magnetization overa range from a room temperature to a Curie temperature Tc. Accordingly,when the laser beam 24 is irradiated, the reproducing layer 16 isincreased in temperature and decreases in coercive force. This causesthe record magnetic domain 22 of the recording layer 14 to betransferred, due to static magnetic coupling, through the intermediatelayer 18 to the reproducing layer 16, thus forming a transferredmagnetic domain (hereinafter referred also to as “seed magnetic domain”)26 within the reproducing layer 16. The transferred or seed magneticdomain 26 is formed at a location corresponding to the record magneticdomain 22. After forming the seed magnetic domain 26 within thereproducing layer 16, an external magnetic field Hep is applied theretoby a not-shown magnetic head, as shown in FIG. 2(B). This externalmagnetic field Hep is an alternating magnetic field, and applied for atleast one period, preferably 2-4 period, while one minimum sizedmagnetic domain is passing through a hot spot 24 a (see FIG. 3) formedby the laser beam 24. If the alternating or external magnetic field Hepapplied is in a same direction (same polarity) as the transferredmagnetic domain 26, the seed magnetic domain 26 is enlarged inmagnetic-domain diameter to provide enlarged magnetic domains 26 a and26 b, resulting in transfer of the record magnetic domain 22 throughenlargement. If a reproducing laser beam is irradiated to thetransferred magnetic domain 26 and the enlarged magnetic domains 26 aand 26 b by using an optical head (not shown), a state of magnetizationin the reproducing layer 16, i.e. a record signal, is reproduced.

[0008] In such a magneto-optical recording medium, there is tendency oftransfer error to occur as the size of the record magnetic domain 22within the recording layer decreases in size. This is due to decrease ofresolution as the transferred magnetic domain area 26 within thereproducing layer 16 becomes greater than the diameter of the recordmagnetic domain. On the other hand, the size of the transferred magneticdomain 26 of the reproducing layer 16 is determined by the size of a hotspot of the laser beam 24. In order to increase the record density bydecreasing the size of the record magnetic domain 22, there is anecessity of decreasing the size of the hot spot 24 a of the laser beam24, that is, the size of the transferred magnetic domain 26 within thereproducing layer 16.

[0009] The laser beam has a temperature profile variable depending uponan output of the laser beam. Accordingly, the decrease in size of thehot spot 24 a only require the reduction in output of the laser beam 24.However, the laser beam output has an effect upon reproducibility, whichhas to be taken into consideration for optimal setting.

[0010] In any of the prior arts, however, nothing has been considered asto optimize the laser beam output from such a point of view.

SUMMARY OF THE INVENTION

[0011] Therefore, it is a primary object of this invention to provide amagneto-optical recording medium and recording/reproducing apparatusused therefor, which can optimize the output of a laser beam.

[0012] It is another object of this invention to provide amagneto-optical recording medium and recording/reproducing apparatusthat can further enhance the recording density.

[0013] A magneto-optical recording medium according to this invention,which allows a magnetic domain in a recording layer to be transferred,through enlargement, to a reproducing layer raised in temperature byirradiation of a laser beam, comprises: a calibration area including acalibration magnetic domain recorded in a predetermined pattern in therecording layer.

[0014] The calibration magnetic domain may include an isolated magneticdomain recorded at an interval not to detect at a same time the magneticdomain in plurality of number.

[0015] A reproducing apparatus according to this invention, comprises:an optical head for irradiating the laser beam to the magneto-opticalrecording medium and reproducing the calibration magnetic domain tooutput a reproduced signal; and an output adjusting means for causingthe optical head to adjust an output of the laser beam depending uponthe reproduced signal.

[0016] This invention is, further, a recording/reproducing apparatus fora magneto-optical recording medium including a recording layer and areproducing layer, comprising: a recording means for recording acalibration magnetic domain in a predetermined pattern in the recordinglayer by means of a magnetic head; a transfer means for transferring thecalibration magnetic domain to the reproducing layer by irradiating alaser beam; a reproducing means for reproducing a transferredcalibration magnetic domain transferred to the reproducing layer tooutput a reproduced signal; and a laser output adjusting means foradjusting an output of the laser beam depending upon the reproducedsignal.

[0017] A calibration area is formed on the magneto-optical recordingmedium. This calibration area may be previously formed. Where using arecording/reproducing apparatus, calibration areas can be provided. Themagneto-optical recording medium is formed by 2. A magneto-opticalrecording medium according to claim 1, wherein the calibration magneticdomain includes an isolated magnetic domain recorded at an intervalgreater than a spot diameter of the laser beam.

[0018] The calibration area includes calibration magnetic domains formedat an interval of a given distance or greater (specifically, at aninterval not to detect at a same time the magnetic domain in pluralityof number).

[0019] By reproducing the calibration magnetic domain in the calibrationarea, the output adjusting means adjusts the output of the laser beamdepending upon the reproduced signal, to thereby set (optimize) a laserbeam output by which a transferred magnetic domain area formed in thereproducing layer is minimized.

[0020] According to this invention, since the laser beam output can beoptimized, the recording in the recording layer is possible with higherdensity.

[0021] The above described objects and other objects, features, aspectsand advantages of the present invention will become more apparent fromthe following detailed description of the present invention when takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a sectional illustrative view showing one example of amagneto-optical recording medium employed in this invention;

[0023]FIG. 2 is an illustrative view showing a method to reproducemagnetic domains recorded in a recording layer of the magneto-opticalrecording medium of FIG. 1, wherein FIG. 2(A) shows a state beforeenlargement while FIG. 2(B) a state after enlargement;

[0024]FIG. 3 is an illustrative view showing, together with temperaturedistribution, a spot of a laser beam irradiated for reproduction usingthe magneto-optical recording medium;

[0025]FIG. 4 is a block diagram showing one embodiment of thisinvention;

[0026]FIG. 5 is a circuit diagram showing one example of a laser drivecircuit in the FIG. 4 embodiment;

[0027]FIG. 6 is an illustrative view showing one example of arrangementof a calibration area formed according to this invention or previouslyon an optical disc;

[0028]FIG. 7 is an illustrative view showing another embodiment ofarrangement of a calibration area formed according to this invention orpreviously on the optical disc;

[0029]FIG. 8 is an illustrative view showing still further embodiment ofarrangement of a calibration area formed according to this invention orpreviously on the optical disc;

[0030]FIG. 9 is an illustrative view showing another embodiment inarrangement of a calibration area formed according to this invention orpreviously on the optical disc;

[0031]FIG. 10 is an illustrative view showing an external magnetic field(pulses) outputted from a magnetic head when forming a calibrationlayer;

[0032]FIG. 11 is an illustrative view showing recorded magnetic domainsformed at the calibration area in the recording area;

[0033]FIG. 12 is a flowchart showing a calibration mode in the FIG. 4embodiment; and

[0034]FIG. 13 is wave form diagrams of a reproduced signal,respectively, showing that the reproduced signal is varied in the numberof peaks in response to variation in output of a laser beam in the FIG.4 embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Referring to FIG. 4, a recording/reproducing apparatus 30 for amagneto-optical recording medium in this embodiment includes a spindlemotor 32 to rotate a magneto-optical recording medium or optical disc10. This spindle motor 32 is controlled by a servo circuit 34. At theabove of the magnet-optical recording medium or disc 10, a magnetic head36 is provided out of contact with the disc 10. A similar optical headis provided at the beneath of the disc 10. The magnetic head 36 isutilized not only to form record magnetic domains 22 (FIG. 2) within arecording layer 14 (FIG. 1) of the disc 10 but also to apply analternating magnetic field for enlarging a magnetic domain 26transferred to a reproducing layer 16. The optical head 38 includes, aswell known, a laser device, a light receiving device, a polarizing beamsplitter, and so on. The laser device (not shown) irradiates a laserbeam onto the magneto-optical recording medium or disc 10 duringreproduction, as stated before. Meanwhile, the light receiving device,e.g. photo-diodes, of two in number detect respective reflected beamsdifferent in polarization axis, depending upon a magnetizing polarity ofa record or transferred magnetic domain (enlarged magnetic domain),thereby outputting a reproduced signal (RF signal).

[0036] The reproduced signal from the optical head 38 is supplied to areproduced signal amplifying circuit 40. The reproduced signalamplifying circuit 40 supplies a tracking-error signal and afocussing-error signal contained in the reproduced signal to a servocircuit 34. The servo circuit 34 controls the spindle motor 32 to rotateat a predetermined rotational speed depending upon the tracking andfocussing signals as well as a clock signal (stated later). The servocircuit 34 also controls movement of an objective lens (not shown)included in the optical head 38. That is, the servo circuit 34 performstracking servo and focussing servo.

[0037] The reproduced signal, amplified by the reproduced signalamplifying circuit 40, is also subjected to integration by a low-passfilter 42 and then supplied to a PLL (Phase-Locked Loop) 44 as a clockgenerating circuit and to a decoder 46. The PLL 44 adjusts the phase andfrequency of an oscillation clock according to a comparison in phasebetween a reproduced clock contained in the reproduced signal and anoscillation clock from a VCO (Voltage-Controlled Oscillator: not shown),to thereby output the oscillation clock as a system clock. This systemclock is supplied to the servo circuit 34 as stated before, and also toa control circuit 48 and the decoder 46.

[0038] The decoder 46 decodes an output signal (reproduced signal) fromthe low-pass filter 42 according to the clock, thereby outputtingreproduction data.

[0039] The control circuit 48 controls a magnetic head driving circuit52 and a laser driving circuit 54, under the control of a micro-computer50. The magnetic head driving circuit 52 includes a pulse signal source(not shown) to generate a pulse signal for writing a record magneticdomain into the recording layer 14 (FIG. 1) through the magnetic head36, and an alternating current signal source (not shown) to generate analternating magnetic field by the magnetic head 36.

[0040] That is, to the control circuit 48 is supplied modulated recorddata so that the control circuit 48 supplies a signal to the magnetichead driving circuit 52 according to the modulated record data. Inresponse thereto, the magnetic head driving circuit 52 controls thepulse signal source to supply a drive signal to the magnetic head 36such that a record magnetic domain is recorded into the recording layerof the magneto-optical recording medium or disc 10 in compliance withthe record data. Incidentally, the frequency of an alternating currentoutputted by an alternating signal source, i.e. alternating magneticfield, is for example at 2.0 MHz in this embodiment. It is, however,possible to arbitrarily alter the frequency.

[0041] The laser driving circuit 54, as shown in detail in FIG. 5,includes a resistance circuit 541 having a plurality of resistanceelements R1, R2, R3, . . . connected in series between a power supplyVcc and a ground. The resistors R1, R2, R3, . . . have series connectingpoints, the respective of which are connected with fixed contacts S1,S2, S3, . . . of a switch 542. The switch 542 has a movable contact C tobe switched over to any of the fixed contacts S1, S2, S3, . . .according to a switching signal supplied from the control circuit 48.Through the movable contact C of the switch 542 is outputted a differentvoltage depending upon which fixed contact is connected to the samecontact. The output voltage of the switch 542 is supplied, through anamplifier 543, to a base of a transistor 544. A laser device 545 isconnected between a collector of the transistor 544 and the power supplyVcc. The transistor 544 has an emitter grounded through an emitterresistance.

[0042] In this laser driving circuit 54, when the movable contact C ofthe switch 542 is changed over by the control circuit 48, an outputvoltage of the amplifier 543, i.e. a base voltage of the transistor 544,is varied thereby to vary a drive current to be flowed through the laserdevice. It is therefore possible to adjust an output of a laser beamgiven from the laser device 545.

[0043] Meanwhile, the reproduced signal, having passed through thelow-pass filter 42, is supplied to a count circuit 58. This countcircuit 58 counts the number of peaks contained in the reproduced signal(corresponding to one polarity of an alternating magnetic field appliedby the magnetic head 36), as will be explained in detail later.Specifically, the count circuit 58 includes a waveform-shaping circuitfor converting the reproduced signal into a pulse signal, and a counterfor counting on the pulse signal outputted from this equalizer. Thevalue counted by the counter is supplied to the micro-computer 50. Themicro-computer 50 supplies a command signal to the control circuit 48depending upon the count value, as explained later, and controls a drivecurrent to the laser driving circuit 54, i.e. laser beam output.

[0044] In the recording/reproducing apparatus 30 in this embodiment, acalibration area 11 is formed on the magneto-optical recording medium ordisc 10, as shown in FIG. 6 to FIG. 9. The calibration area 11 is anarea to adjust an output of an laser beam by reproducing a record signalcontained the same area. Note that, where employing an apparatus havingno recording function, i.e. an reproduction-exclusive apparatus, it ispossible to utilize a magneto-optical recording medium or discpreviously formed with such calibration areas.

[0045] In an embodiment of FIG. 6, a calibration area 11 is formed at alocation immediately behind a TOC area on the disc 10. In an embodimentof FIG. 7, a calibration area 11 is formed at an innermost of the disc10. In an embodiment of FIG. 8, calibration areas 11 are formed atrespective locations of immediately behind a TOC area and the innermostof the disc 10. In an embodiment of FIG. 9, calibration areas 11 are setat respective beginnings of zones on the disc 10.

[0046] By utilizing a disc 10 having such calibration areas 11,calibration or laser beam output adjustment can be effected at desiredtiming. For example, an optimal output of a laser beam can be determinedby effecting a calibration at a time of initializing the disc.Otherwise, calibration can be carried out when loading a disc onto arecording/reproducing apparatus or a reproducing apparatus. Inparticular, if the disc of FIG. 9 be utilized, the laser beam output canbe optimized by calibrations each time any of the zones comes toreproduction.

[0047] Now, explanations will be made for a method to form a calibrationarea in the FIG. 4 embodiment. To form a calibration area, themicro-computer 50 sets a calibration-signal recording mode. In thismode, the micro-computer 50 sends a command signal to the controlcircuit 48 to output a calibration signal. In response thereto, thecontrol circuit 48 enables the pulse signal source (not shown) of themagnetic head driving circuit 52. Consequently, the magnetic headdriving circuit 52 supplies a pulse signal as shown in FIG. 10 to themagnetic head 36. That is, the magnetic head 36 responds to anintermittent pulse signal as shown in FIG. 10 to apply an externalmagnetic field to the disc 10. Accordingly, recorded magnetic domains 22are created within the recording layer 14 (FIG. 1) on the disc 10, asshown in FIG. 11. The record magnetic domains 22 have a sizecorresponding to a minimum magnetic domain recordable on the disc, andan interval therebetween selected near equal to or greater than a spotdiameter 24 a (FIG. 2) of a laser beam 24. That is, calibration-signalmagnetic domains, which are to be recorded at a calibration area 11 inthe recording layer 14, are isolated magnetic domains formed at aninterval greater than the spot diameter of the laser beam. Note that, inthe FIG. 11 embodiment, the record magnetic domains has a size, forexample, of approximately 0.1-0.2 μm, and at an interval, for example,of 0.8 μm or greater.

[0048] Now, a calibration mode will be explained with reference to FIG.12 and FIG. 13, in which a laser beam is optimized in output(calibration) by using a disc 10 formed with a calibration area 11 (FIG.6 to FIG. 9). FIGS. 13(A), (B) and (C) respectively demonstratereproduced signal waveforms observed when the output of a laser beam isvaried as, e.g. 1.4 mW, 1.2 mW and 1.0 mW, with the frequency of anexternal alternating magnetic field Hep kept at constant.

[0049] In the calibration mode, when a disc 10 is loaded, themicro-computer 50 sets, at a first step S1, a frequency of analternating external magnetic field Hep (FIG. 3) outputted from themagnetic head 36. Although this frequency can be desirably set as statedbefore, the frequency in this embodiment is set at 2.0 MHz. Then, themicro-computer 50, at next step S2, makes initial setting of an outputPr of reproducing power of laser beam 24. Although this initial outputvalue is set at approximately 0.6 mW, this initial value also can bedesirably set.

[0050] After making the initial setting as above, the micro-computer 50at a step S3 performs reproduction on the calibration magnetic domainrecorded as stated before in the calibration area 11 (FIG. 6 to FIG. 9).That is, the micro-computer 50 enables the laser driving circuit 54through the control circuit 48, in a manner similar to a usualreproduction, to thereby drive the laser device 545 (FIG. 5) at theinitial power set at the step S2. The driving the laser device 545causes the magnetic head 38 to output a laser beam 24 (FIG. 2).Consequently, the calibration magnetic domain 22 in the recording layer14 is transferred to the reproducing layer 16 as explained before, thusforming a seed magnetic domain within the reproducing layer 16, due to acalibration magnetic domain. Then the micro-computer 50 sends a commandsignal to the control circuit 48. Accordingly, the magnetic head 36produces an alternating magnetic field at an output set by the step S1.As the intensity of the magnetic field exceeds a magnetic domain-wallcoercive force Hw, the seed magnetic domain 26 is enlarged to formenlarged magnetic domain portions 26 a and 26 b. That is, thecalibration magnetic domain is transferred through enlargement. Inresponse to a laser beam output at that time, a reproduced signal isprovided through the optical head 38, for example as shown in FIG. 13(A)to FIG. 13(C). This reproduced signal has peaks in number dependent uponthe frequency of the alternating magnetic field. More specifically, whena laser beam 24 is irradiated, a seed magnetic domain 26 is createdwithin the reproducing layer 16 due to a leak magnetic field from therecording layer 14 through the intermediate layer 18. This seed magneticdomain 26 turns into an enlarged magnetic domain of from 26 a to 26 b,for example, by a positive-polarity magnetic field of the externalalternating magnetic field Hep, thus forming peaks in the reproducedsignal.

[0051] The number of peaks in the reproduced signal is counted by theabove-stated count circuit 58, and a value N of the count is inputted,at a step S4, to the micro-computer 50.

[0052] The micro-computer 50 determines, at a next step S5, whether ornot the count value N is “0”, i.e. N=0?. If N is not “0”, themicro-computer 50 sets, at a next step S6, the output Pr of the laserbeam 24 to “Pr−ΔP” (Pr=Pr−ΔP). At this time, the decrement value “ΔP” ofthe output is set, for example, at approximately 0.2 mW-0.5 mW. That is,the count value N of not “0” is to be considered as excessively highlaser beam power. Accordingly, the micro-computer 50 at a step S6decrements the laser beam power by a constant amount for each time. At astep S7, the calibration area 11 is again reproduced similarly to thestep S3, and the count value N is fetched from the count circuit 58,similarly to the step S4. At a step S9, a determination of N=0? isexecuted, similarly to the step S5. At this step S9, if thedetermination is “YES”, the micro-computer 50 at a next step S10increments the power of the laser beam 24 (Pr=Pr+ΔP). The outputincrement value “ΔP” at this time is set, for example, at approximately0.2 mW-0.5 mW. However, the value may be the same as the decrementvalue, or to a different value. At the step S9, if “NO” is determined,the micro-computer 50 returns to the step S6, to repeat the steps S6-S9.

[0053] That is, at the steps S6-S9, the micro-computer 50 determines anoutput Pr of the laser beam 24 at which the count value N of the countcircuit 58, i.e. the number of peaks in the reproduced signal, becomes“0”. If the count value N becomes “0”, the output of the laser beam isincreased at a step S10. By executing the steps S6-S9, the output of thelaser beam is adjusted until the number of peaks of the reproducedsignal, i.e. the count value N of the count circuit 58, becomes aminimum value other than “0”. For example, in the embodiment of FIG. 13the laser beam power set by the step S10 may be 1.0 mW.

[0054] If the count value N is “0” at the step S5, the micro-computer 50sets, at a next step S11, the output Pr of the laser beam 24 to “Pr+ΔP”(Pr=Pr+ΔP). Since the count value N of “0” means a low output of thelaser beam, the micro-computer 50 increments, at a step S11, the laserbeam power by a constant amount for each time. Then, the micro-computer50 again reproduces, at a step S12, a calibration area 11 similarly tothe step S3 or S7, and then fetches the count value N from the countcircuit 58 at a step S13. It is determined if N=0? at a step S14. If thedetermination is “YES” at this step S14, the micro-computer 50 returnsto the step S11 to repeat the steps S11-S14.

[0055] That is, by executing the steps S11-S14, the micro-computer 50makes adjustment on the laser beam output until the count value N of thecount circuit 58, i.e. the number of peaks in the reproduced signal,reaches a minimum value other than “0”.

[0056] Incidentally, in the example of FIG. 12, the minimum value otherthan “0” is “1” because the number of peaks and the reproduced signaldecreases as “3”, “2” and “1” as the laser beam output is graduallydecreased. However, there is a case that the minimum value for thenumber of peaks other than “0” is at “2” or greater. For example, thisis true for a case that the number of peaks varies as “4”, “3”, “2”, “0”as the laser beam power decreases. In such a case, the micro-computer 50determines the laser beam output at which the number of peaks is at “2”.

[0057] In this manner, the optimization of the laser beam 24 (FIG. 3)output enables setting the size of a transferred magnetic domain area 26in the reproducing layer to a required minimum, during reproduction. Itis therefore possible to reduce the size of the magnetic domain in therecording layer 14 to a minimum extent, thereby realizing recordationwith higher density.

[0058] Incidentally, the above embodiment used, as a reproducing layer,the magnetic layer assuming as a magnetic thin film with perpendicularmagnetization in a temperature range of at least from a room temperatureto a reproduction temperature. However, this reproducing layer may be bya magnetic layer assuming a magnetic thin film with in-planemagnetization at a normal temperature and a magnetic thin film withperpendicular magnetization at a raised temperature. In this case, theremay be a case that an alternating external magnetic field is unnecessaryto apply in order to enlarge the magnetic domain.

[0059] Although the present invention has been described and illustratedin detail, it is clearly understood that the same is by way ofillustration and example only and is not to be taken by way oflimitation, the spirit and scope of the present invention being limitedonly by the terms of the appended claims.

What is claimed is:
 1. A magneto-optical recording medium which allows amagnetic domain in a recording layer to be transferred, throughenlargement, to a reproducing layer raised in temperature by irradiationof a laser beam, comprising: a calibration area including a calibrationmagnetic domain recorded in a predetermined pattern in said- recordinglayer.
 2. A magneto-optical recording medium according to claim 1 ,wherein the calibration magnetic domain includes an isolated magneticdomain recorded at an interval not to detect at a same time the magneticdomain in plurality of number.
 3. A magneto-optical recording mediumaccording to claim 1 , wherein the calibration magnetic domain includesan isolated magnetic domain recorded at an interval greater than a spotdiameter of the laser beam.
 4. A magneto-optical recording mediumaccording to claim 3 , wherein the isolated magnetic domain is a minimummagnetic domain recordable in said magneto-optical recording medium. 5.A reproducing apparatus for reproducing from a magneto-optical recordingmedium on which a laser beam is irradiated to transfer, throughenlargement, a magnetic domain in a recording layer to a reproducinglayer raised in temperature, wherein said magneto-optical recordingmedium has a calibration area including a calibration magnetic domainrecorded in a predetermined pattern in said recording layer, comprising:an optical head for irradiating the laser beam to said magneto-opticalrecording medium and reproducing the calibration magnetic domain tooutput a reproduced signal; and an output adjusting means for causingsaid optical head to adjust an output of the laser beam in response tothe reproduced signal.
 6. A reproducing apparatus according to claim 5 ,wherein the calibration magnetic domain of said magneto-opticalrecording medium includes an isolated magnetic domain recorded at aninterval not to detect at a same time the magnetic domain in pluralityof number by the laser beam.
 7. A reproducing apparatus according toclaim 6 , wherein the isolated magnetic domain is a minimum magneticdomain recordable on said magneto-optical recording medium.
 8. Areproducing apparatus according to any of claims 5 to 7 , wherein saidreproducing layer comprises a magnetic layer assuming a magnetic thinfilm with perpendicular magnetization in a range of at least from a roomtemperature to a reproducing temperature, further comprising a magnetichead for generating an alternating magnetic field to enlarge atransferred calibration magnetic domain transferred to said reproducinglayer, wherein said optical head has a laser device to output the laserbeam, and outputs the reproduced signal in level in response to anintensity of the laser beam; said output adjusting means includes anintensity detecting means for detecting an intensity of the reproducedsignal, and a drive power control means for controlling drive power tosaid laser device in response to the intensity.
 9. A reproducingapparatus according to claim 8 , wherein the reproduced signal has peaksin number corresponding to the alternating magnetic field, the intensitydetecting means includes a number detecting means for detecting a numberof peaks contained in the reproduced signal, said drive power controlmeans applying a driving power at which the peaks become minimum innumber to said laser device.
 10. A reproducing apparatus according toany of claims 5 to 7 , wherein said reproducing layer is formed by amagnetic layer assuming as a magnetic thin film with a planarmagnetization at a normal temperature and a magnetic thin film withvertical magnetization at a increased temperature, further comprising amagnetic head for generating an alternating magnetic field to enlarge atransferred calibration magnetic domain transferred to said reproducedlayer, wherein said optical head has a laser device to output the laserbeam, and outputs the reproduced signal having a level in response to anintensity of the laser beam, said output adjusting means including anintensity detecting means for detecting an intensity of the reproducedsignal, and a drive power control means for controlling a drive power tosaid laser device in response to the intensity.
 11. A reproducingapparatus according to claim 10 , wherein the reproduced signal haspeaks in number corresponding to the alternating magnetic field, saidintensity detecting means including a number detecting means fordetecting a number of peaks contained in the reproduced signal, saiddrive power control means applying a drive power at which the peaksbecomes minimum in number to said laser device.
 12. Arecording/reproducing apparatus for a magneto-optical recording mediumincluding a recording layer and a reproducing layer, comprising: arecording means for recording a calibration magnetic domain in apredetermined pattern in said recording layer by means of a magnetichead; a transfer means for transferring the calibration magnetic domainto said reproducing layer by irradiating a laser beam; a reproducingmeans for reproducing a transferred calibration magnetic domaintransferred to said reproducing layer to output a reproduced signal; anda laser output adjusting means for adjusting an output of the laser beamdepending upon the reproduced signal.
 13. A recording/reproducingapparatus according to claim 11 , wherein said reproducing layer isformed by a magnetic layer assuming a magnetic thin film with verticalmagnetization in a range of from a room temperature to a reproducingtemperature, said magnetic head generating an alternating magnetic fieldto enlarge the transferred calibration magnetic domain, furthercomprising an optical head including a laser device to output the laserbeam, said optical head outputting the reproduced signal having anintensity in response to an output of the laser beam, and said outputadjusting means including an intensity detecting means for detecting theintensity of the reproduced signal and a drive power control means forcontrolling a drive power to said laser device in response to theintensity.
 14. A recording/reproducing apparatus according to claim 13 ,wherein the reproduced signal has peaks in number corresponding to thealternating magnetic field, said intensity detecting means including anumber detecting means for detecting a number of peaks contained in saidreproduced signal, and said drive power control means applying a drivepower at which the peaks become minimum in number to said laser device.15. A recording/reproducing apparatus according to claim 11 , whereinthe reproducing layer is formed by a magnetic layer assuming as amagnetic thin film with planar magnetization at a normal temperature anda magnetic thin film with vertical magnetization at a raisedtemperature, said magnetic head generating an alternating magnetic fieldto enlarge the transferred calibration magnetic domain, furthercomprising an optical head including a laser device to output a laserbeam, said optical head outputting the reproduced signal having anintensity in response to an output of the laser beam, said outputadjusting means including an intensity detecting means for detecting theintensity of the reproduced signal and a drive power control means forcontrolling a drive power to said laser device in response to theintensity.
 16. A recording/reproducing apparatus according to claim 15 ,wherein the reproduced signal has peaks in number corresponding to thealternating magnetic field, said intensity detecting means including anumber detecting means for detecting a number of peaks contained in thereproduced signal, and said drive power control means applying a drivingpower at which the peaks become minimum in number to said laser device.